Citalopram is an important anti-depression drug, which is a selective 5-hydroxytryptamine (5-HT) reuptake inhibitor with S-configuration, and the isomer with S-citalopram has an anti-depression effect that is 100 times more than the isomer of the opposite configuration—R-citalopram, therefore, it has a much better curative effect and much less dosage. In the market of Europe and America, the S-isomer is mainly sold, and it is prepared by the cyclization and salt-forming reaction of S-5-cyano diol (IV).
S-5-cyano diol (IV) is the key initial raw material for producing S-citalopram, in industrial production, generally, it is prepared by forming a salt from racemic 5-cyano diol (I) and a resolving agent D-(+)di-p-toluoyl tartaric acid (II) (abbr. DPTTA) in alcohols and mixed solvents comprising alcohols, separating the (S)-5-cyano diol resolved intermediate (Ill) by crystallization, then subjecting to ionization by a free base. The resolution process can be represented as follows:

The structure of the resolving agent DPTTA is as follows:

In U.S. Pat. No. 4,943,590 and WO2007012954, it is described that the (S)-5-cyano diol resolved intermediate (III) is obtained by the resolution of racemic 4-(4-dimethylamino-1-p-fluorophenyl-1-hydroxybutyl)-3-(hydroxymethyl) benzonitrile by DPTT in isopropanol. The particle size of the crystals of the (S)-5-cyano diol resolved intermediate (III) obtained by the method are small and they are hard to be filtered, which does not meet the requirement of large-scale industrial production, and the chiral purity of the obtained crude (S)-5-cyano diol resolved intermediate (III) is low, the crude product needs to be repurified by isopropanol during the production to be qualified, thus the operation is very complex.
US20090069582 reports the preparation of the (S)-5-cyano diol resolved intermediate(III) with DPTT as the resolving agent, resolving racemic 5-cyano diol (I) from the solvent system comprising 1-propanol. The chiral purity of the method is generally low, two times of refinements are needed during production to obtain the (S)-5-cyano diol resolved intermediate (III) with qualified chiral purity, and the yield of the method is smaller than 38% at present.